# Persist() fails with PersistentObjectException on ManyToOne field

**URL:** <https://discourse.hibernate.org/t/persist-fails-with-persistentobjectexception-on-manytoone-field/4011>\
**Category:** Hibernate ORM\
**Created:** [April 10, 2020, 8:45pm UTC](https://discourse.hibernate.org/t/persist-fails-with-persistentobjectexception-on-manytoone-field/4011 "2020-04-10T20:45:00Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![micpalmia](https://yyz1.discourse-cdn.com/flex035/user_avatar/discourse.hibernate.org/micpalmia/32/1022_2.png) [@micpalmia](https://discourse.hibernate.org/u/micpalmia)\
**Post date:** [April 10, 2020, 8:45pm UTC](https://discourse.hibernate.org/t/persist-fails-with-persistentobjectexception-on-manytoone-field/4011/1 "2020-04-10T20:45:00Z")

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I’ve been trying to wrap my head around Hibernate for a few days now and I think I’ve hit a corner.

I have an entity with a field annotated as `@ManyToOne` and that I initially designed to use a composite `@EmbeddedId`. The ManyToOne annotation is unidirectional because the parent would have far too many children to be meaningful in any way.

If I try to persist the entity and I pass its parent (previously fetched in another session) to it, everything works fine - but the parent is fetched again from db before the insert happens. **Why is the parent instance fetched from db?** (The logs seem to imply that a cached copy could not be found? what does that mean? I passed a copy straight out of storage to it).

In an effort to avoid the additional select, I tried making my entity `Persistable`. This made things worse, as the call to persist (via Spring Data JPA’s save) failed with the typical `detached entity passed to persist` exception. Surprisingly though, this was on the field annotated with `@ManyToOne`! **Isn’t there supposed to be no cascading by default on @ManyToOne?!**

If id get rid of the `@Embedded` id and instead use a standard `@Id` with `@GeneratedValue (strategy = IDENTITY)`, everything works as expected - and no additional fetches are performed - but now I have one more column in my db!

Can someone point me towards why I am observing this behavior? Thanks! 🙏🏻